Mounting of electrodes in electric discharge tubes



March 11 1947.

A. L. CHILCOT ET AL MOUNTING OF'ELECTRODES IN ELECTRIC DISCHARGE TUBES Filed Dec. 24:, 1943 nventom; MM z /Q/CM B'y A ttorney.

Patented Mar. 11, 1947 MOUNTING OF ELECTRODES 1N ELECTRIC DISCHARGE TUBES Arthur Leslie Chilcot, Timperely, Sydney Jackson, Chadderton, and Frank Warburton Taylor, Oldham, England Application December 24, 1943, Serial No. 515,502

In Great Britain April 18, 1942 19 Claims. (01. 250-275) This invention relates to electric discharge tubes of the kind in which at least one electrode is mounted at each end of the envelope, and hereinafter is identified as the kind referred to."

For certain purposes, discharge tubes of the usual type, in which all the electrodes are carried by a common pinch or foot, are undesirable. Ex amples of such purposes are where discharge tubes are required to withstand high mechanical stress, or to operate under such a condition, or for shortwave work, where inter-electrode capacity must be as low as possible, and for these purposes a tube of the kind referred to is to be preferred. Where the discharge tube has a cathode activated by the deposition thereon of an alkali metal, it is also highly desirable that the tube be of the double-ended type in order that the cathode may be maintained at low temperature whilst other parts of the tube are heated to ensure that the alkali metal is deposited only on the cathode.

Where such discharge tubes are produced in quantity by mass production it has hitherto been found necessary to use such means as insulating inter-electrode spacers in order to obtain products having characteristics which vary as little as possible from one another. If such means are not employed wide variations of characteristics are difiicult to avoid due to relatively small variations of spacing, particularly transverse spacing of the electrode. Where the cathode is to be activated as described above, such inter-electrode spacers are objectionable owing to the likelihood of the formation thereon of conducting films which would cause electrical leakage between the electrodes held by the spacers.

The main object of the present invention is to provide a form of construction of electric discharge tube of the kind referred to which ensures that all products of the same manufacturing process are as nearly identical as possible to one another in respect of their characteristics and which avoids the use of inter-electrode spacers.

The characteristics of such tubes, as already stated, are to a very great, extent dependent on the spacing. particularly the transverse spacing, between electrodes and the aim of the invention is to ensure that such spacing is determined accurately without the use of inter-electrode spacers. Thus any slight variations in the characteristics which maystill-occur between thev several products made in accordance with the invention will be mainly those which arise from other factors, such as the chemical nature of the oathode surface.

The invention is particularly useful for socalled midget tubes.

According to the invention an electric discharge tube has a glass envelope formed from two cup-like portions joined together each of which is provided at pre-selected parts with internal protuberances by reference to at least some of the apices of which at least one electrode, which is carried by one of the said cup-like portions, is accurately located and at least some of which apices servelto prevent both lateral and tilting displacement of another electrode carried by the other of the said cup-like portions, whereby the said electrodes are accurately located in desired spatial relationship to one another.

Also in accordance with the invention a metho of constructing an electric discharge tube includes the fixing into each of two glass cup-like members of an electrode which, during the fixing process, is prevented from undergoing lateral displacement by the apices of a set of protuberances formed on pre-selected parts of the inner surface of the cup-like member to which the said electrode is fixed and which is also prevented from undergoing tilting displacement by additional locating means integral with the said cup-like member, and forming the. envelope of the discharge tube by joining the said cup-like members together in such a manner that one of the said electrodes is positioned laterally by contact thereof with the apices of the protuberances on the cup-like member to which it is not fixed and is prevented from undergoing tilting displacement by the said additional locating means of the last-mentioned cup-like member, whereby said electrodes are accurately positioned in desired spatial relationship to one another.

According to an aspect of the invention as set forth in theimmedia'tely preceding paragraph, the said additional locating means comprises an integral flange at the open end of at least one of the said cup-like members, said flange having a flat face lying in a place normal to a longitudinal axis of the said cup-like member to which axis the aforesaid protuberances are spatially related.

According to another aspect of the invention as set forth in the next but one preceding paragraph, the said additional locating means comprises a further set of protuberances formed on the inner surface of at least one of each of the said cup-like members, the apices of which further set of protuberances are so disposed as to prevent tilting displacement in co-operation with the apices of the first-mentioned set of protuberances which serve to prevent lateral displacement. I H According to a. further aspect of the invention as set forth in the first of the three immediately preceding paragraphs, the said additional locating means includes the formation of steps on some of 1 the said set of protuberances, which stepsare adapted to prevent longitudinal movement-of the associated electrode or jig as the case may be to provide full spatial relationship;

one of the cup-like members andla's'sociatecl ele'-.' ments in an early stage of manufacture" of: a

tube; Figure 2 is a similar. view showing an electrode in position in said cup prior to sealing-in h i I Figure 3 is a vertical cross-sectional view of the other cup-like member showing an electrode in position prior to sealing-in thereof Figure 4 is a vertical cross-sectional -view of the assembly of the two cup like members with the electrodes in thedesiredspatial relationship and constituting the completed tube; 5 Figures 5, 6 and 7 are views similar to Figure 4 illustrating modifications thereof, and Fig. 8 is a fragmentary view showing a bead form of protuberance; f The invention may be carried into effect, ac cording to one form by way of example, in the manufacture of a diodevalve having a tubular anode and a surrounding hollow cylindrical oath ode. Two glass cup-like members; one of which is shown at a in Figure l, which together are to form the envelope, are each provided with an integral flange-at their open'endsj'the'flanges having flat faces lying in planes perpendicular (normal) to the longitudinal axe's'of'the cuplike members. These fiange's'may be formed by moulding during. the manufacture of the cuplike member, or by softening the'rim'of such.a member, flaring to form 'theflflange and" either pressing in a jig whilst soft'or grinding flat when cold. Each cup-like'm'ember'is placed over a I mandrel b the diameter of which is, that of the cathode, and is held in position coaxially with the mandrel by means'of a hollow cone 0 disposed in line with the mandrel into which the dome of the cup-like member fits and by a suitably disposed flat surface d which co-operates with the flat surface of the flange. Three internal protuberances," one of which is shown at e, disposed symmetrically on a circle, are formed on the wall of the cup-like member by'local heating to softening point and separate indentation with a suitable'tool, the glass being allowed" to cool between each operation in order to avoid unwanted distortion of the glass. These three protuberances, which form a set, are formed to a height such that their apices come'into contact with mandrel b. A hole is blown through the middle of the domed end of each cup-like member. I

The anode I, see Figure 2, consists of a small tube of nickel, welded to a wire 9 of suitable'material'u on whi'clra'gla'ss" bead h hasbeen" fused.

This anode is held in a jig 2' having an external diameter equal to that of the cathode and also having a co-axial hole to receive and locate the anode and the jig is inserted in contact with the protuberances e in one of the cup-like members a so that the wire 9 passes through the hole in its domed end and with the bead h adjacent thereto. The jig has a flat annular portion 7' in a plane perpendicular to its axis and this bears against the fiat surface of the flange of the cuplike member, thusthe jig. isprevented by the protuberances from undergoing-lateral displacement and by the flange from being tilted so that there is only one position of location of the jig. The

bead h is now fused to the end of the cup-like member, thus supporting the anode rigidly and sealing the hole. Anexhaust tube It is also fused into this same end; When cool, the jig is removed .leaving the anode accurately located with respect' both to the apices of the protuberances, and to the plane of the end of the cup-like member which locating means are together complementary to a locating axis normal to such plane and co-axial with the apices of the protuberances.

The cathode I, see Figure 3, is in the form of a hollow cylinder, having one end closed and a wire m of suitable material welded to the centre of this end, which wire carries a glass bead n. The cathode is supported in an annular slot 0 in a flat platform-p withits axis normal thereto and the other cup-like member a is placed over it so that its flange bears against the platform. The wire m passes through the-hole in the domed end of the cup-like member with the bead n adjacent to it. The cathode is in this manner prevented by the protuberances e formed on'the wall of cup-like member" a in the manner described above, from undergoing lateral displacement and by the flange from being tilted, and is located co-axially witha locating axi-s normal to the plane of the flangeand-co-axial with the apices of the pro-tuberances. Whilst the cathode is thus disposed the head n is fused to the A end of the cup-like member, thereby sealing the hole and supporting the cathode rigidly in the cup-like member in its one and only posssible location. v

The two'cup-like members a and a are now brought together as shown in'Figure 4, until the two flanges bear against one another. The cathode l enters the cup-like member'a carrying the anode f and is positioned laterally 'by contact with the apices'of theprotuberances e on that member; itis also prevented from being tilted with respect to the anode by the fact of being rigidly mounted in its cup-like member and by the bearing of the flanges of the two cup-like members against one another. The two flanges are then fused together near their outer rims to complete the envelope of the discharge tube, while the electrodes remain located in their predetermined spatial relationship as, above described. The tube is then exhausted and activated by any method. I j

In accordance with a modification of the invention as shown in Figure 5, tilting. of each electrode with respect to the cup-like member to which it is fixed is prevented during mounting by the provision of a further set of three protuberances, e disposed symmetrically on a circle on the inner wall of each of the two members. This further 'set of protuberances is formed at a di an a a l fro th et o .r ue n esor e as the-case -maybe, already provided so that both sets of protuberances of each cup-like member are within the length of the cathode. In this construction the jig carrying anode, and the cathode are located positively in their respective cup-like members by eachpair of sets of protuberances e and e or e and e and not by an end plane. Since the flanges serve merely to enable the members to be joined together, they may be formed without the accurate flat end faces required by the method described with reference to Figures 1 to 4. When the two cup-like members are brought together the cathode is positioned by contact with the two sets of protuberances e and e on the cup-like member a to which it is not fixed. Where the parts of Figure 5 are the same as in Figure 4 they are given the same reference characters.

In accordance with another modification of the invention, see Figure 6, tilting is prevented by forming steps q, q on at least some of the protuberances by means of a suitable tool whilst they are soft. The protuberances concerned are disposed in such a manner that when the two cup-like members a and a are joined each end of the cathode l abuts against the steps and is thereby located firmly. The ends of the cathode lie in planes perpendicular to its axis. The joining process is facilitated by disposing the stepped protuberances in such a manner that in order to engage the cathode the two cup-like members have to be pushed together during this process. As in the previous modification, the flanges serve only for joining purposes. Where the parts of Figure-6 are the sameas in Figure 4 they are given the same reference characters.

Instead of stepping the protuberances addi- 'tional protuberances e of greater height (internal projection) than those for locating laterally may be provided, as shown in Figure 7.

The cathode need'not be cylindricaLthe protuberances being provided in such positions and to such heights as to locate with the electrode, whatever configuration it may have. For instance, the rim of the cathode may be flared out to give increased strength and to reduce the effect of the rim on the electrical characteristics of the tube; in this case,,the protuberances which are intended to locate the rim are of less height inwardly than those which locate the body portion of the cathode.

The anode may be mounted asymmetrically relative to the cathode by using an appropriate jig. The hollow cylindrical electrode may be the anode instead of the cathode. Furthermore, one or more additional electrodes may be inserted, being held in the same or other jigs having a diameter equal to that of the cylindrical electrode so as to employ the same principles of location. The cathode may be of either the cold or hot emissive variety and the discharge tube may be gas-filled or evacuated.

Instead of forming the protuberances by indentation, they may be formed by fusing glass beads to the interior of the cup-like member and adjusting such beads in height by inserting a mandrel whilst they are in a plastic, state. Fig. 8 shows a bead e fused to the wall a of the glass envelope to provide a protuberance.

Since only the apices of the protuberances touch the cylindrical electrode, the latter may be heated for degassing purposes without "fusin or cracking the glass envelope; especially is this so where a borosilicate glass is employed.

The set of protuberances serving to prevent lateral I displacement need not be disposed o'n-a circle as described above but may bearranged in any convenient fashion provided lateral displacement is prevented. Similarly the arrangement of protuberances in the case where some of them serve to prevent tilting is also subject to modification if desired;

It will be appreciated that whilst variations may occur in the dimensions of the glass cuplike members, the dispositions of the apices of the protuberances and where provided the flat locating faces of the flanges in the several products,- being formed against accurately machined parts, are reproduced accurately. Since the jig and'the hollow cylindrical electrode, being of metal, may also be formed with considerable accuracy, it is possible to produce discharge tubes in quantity all of them having substantially identical. inter-electrode spatial relationships and hence having substantial uniformity of characteristics subject only to any slight variation due mainly to other factors, such as the chemical nature of the cathode surface.

What we claim is:

1. A method of constructing an electric discharge tube having a glass envelope comprising two portions joined together, each of which carries at least one electrode complementary with an electrode of the other, wherein the said two portions of the envelope are each formed with locating means including inwardly projecting protuberances and relative to which locating means its said electrode can be mounted in only one exactly predetermined location; mounting the said complementary electrodes in each portion of-the envelope in such predetermined locations, said locating means also providing complementary location so that the two said portions with their electrodes, are interlocatin whereby they can only be assembled with such complementary electrodes in one predetermined relative transverse spatial relationship.

2. A method of constructing an electric discharge tube having a glass envelope comprising two portions joined together, each of which carries at least one electrode complementary with an electrode of the other, wherein the said two portions of the envelope are each formed with locating means including (a) inwardly project- 'ing protuberances and (b) inter-engaging plane junction surfaces on the two portions of the envelope normal to a common locating axis for the said electrodes relative'to which locating means each said electrode can be mounted in only one exactly predetermined location, mounting the said complementary electrodes in each portion of the envelope in such predetermined locations and finally joining the said portions together so that one said electrode, mounted in one portion of-the envelope is located by at least some of the said protuberances of the other portion of the envelope and also by the inter-engagement of the said plane junction surfaces.

3..- A. method. of constructing an electric discharge tube having a glass envelope comprising two portions joined together, each of which carries at least one electrode complementary with an electrode of the other, wherein the said two portions of the envelope are each formed with locating means including (a) one set of inwardly projecting protuberances and (b) a further set of inwardly projecting protuberances relative to which locating means, each said electrode can be mounted in" only one exactly predetermined location, mountingthe said complementary electrodes in each" portion ofthe envelope insuch predetermined locations and finally joining the said. portions together so that one said electrode mounted in one portion of the envelope is located by both sets of the said protuberances in the other portion of the envelope.

A method of constructing an electric discharge tube having a glass envelope comprising two portions joined together, each of which carries at least one electrode complementary with an electrode of the other, wherein the said two portions of the envelope are each formed with locating means including (a) inwardly projecting protuberances and (b) the formation of steps on some of the said protuberances relative to which locating means .each said electrode can be mounted in only one exactly predetermined location, mounting the said complementary electrodes in each portion of the envelope in such predetermined locations and finally joining the said portions together so that one said electrode mounted in one portion of the envelope is fully located by at least some of the protuberances and steps in each portion of the envelope.

5. An electric discharge tube having a glass envelope formed from two cup-like portions joined together each of which is provided at pre-selected parts with internal protuberances by reference to at least some of the apices of which at least one electrode, which is carried by one of the said cup-like portions, is accurately located and at least some of which apices serve to prevent both lateral and tilting displacement of another electrode carried by the other of said cup-like portions, whereby said electrodes are accurately located in desired spatial relationship to one another.

6. A method of constructing an electric discharge tube including the fixing into each of two glass cup-like members of an electrode which, during the fixing process, is prevented from undergoing lateral displacement by the apices of a set of protuberances formed on pre-selected parts of the inner surface of the cup-like member to which the said electrode is fixed and which is also prevented from undergoing tilting displacement by additional locating means integral with thesaid cup-like member, and forming the envelope of the discharge tube by joining the said cup-like members together in such a manner that one of the said electrodes is positioned laterally by contact thereof with the apices of the protuberanceson the cup-like member to which it is not fixed and is prevented from undergoing tilting displacement by the said additional locating means of the last-mentioned cup-like member whereby the said electrodes are accurately positioned in desired spatial relationship to one another.

7. A method of constructing an electric discharge tube according to claim 6 wherein the said additional locating means of the last-mentioned cup-like member engages with the said additional locating means of the other cup-like member.

8. A method of constructing an electric discharge tube according to claim 6 wherein the said additional locating means of the last-mentioned cup-like member engages with the electrode carried by the other cup-like member.

9. A method of constructing an electric discharge tube including the fixing into each of two glass cup-like members of an electrode which, during the fixing process, is prevented from undergoing lateral displacement by the apices of a set of protuberances iormed'on pre-selectedparts of the inner surface of the cup-like member to which the said electrode is fixed and which is also prevented from undergoing tilting displacement by additional locating means integral with the said cup-like member, and forming the envelope of the discharge tube by joining the said cup-like members together in such a manner that one of the said electrodes is positioned laterally by contact thereof with the apices of the pro tuberances on the cup-like member to which it is not fixed and is prevented from undergoing tilting displacement by the said additional locating means of the last-mentioned cup-like member, whereby the said electrodes are accurately positioned in desired spatial relationship to one another, and wherein the said additional locating means comprises an integral flange at the open end of at least one of the said cup-like members, the said flange having a fiat face lying in aplane perpendicular (normal) to a longitudinal axis of the said cup-like member to which axis the protuberances are spatially related.

10. A method of constructing an electric discharge tube including the fixing into each of two glass cup-like members of an electrode which, during the fixing process, is prevented from undergoing lateral displacement by the apices of a set of protuberances formed on pre-selected parts of the inner surface of the cup-like member to which the said electrode is fixed and which is' also prevented from undergoing tilting displacement by additional locating means integral with the said cup-like member, and forming the envelope of the discharge tube by joining the. said cup-like members together in such a manner that one of the said electrodes is positioned laterally by contact thereof with the apices of the protuberances on the cup-like member to which it is not fixed and is prevented from undergoing tilting displacement by the said additional locating means of the last mentioned cup-like member, whereby the said electrodes are accurately positioned in desired spatial relationship to one another, and wherein the said additional locating means comprises a further set of protuberances formed on the inner surface of at least one of the said cup-like members, the apices of which further set of protuberances are so disposed as to prevent tilting displacement in co-operation with the apices of the first-mentioned set of protuberances which serve to prevent lateral displacement. 1

11. A method of constructing an electric discharge tube including the fixing into each of two glass cup-like members of an electrode which, during the fixing process, is prevented from undergoing lateral displacement by the apices of a set of protuberances formed on pro-selected parts of the inner surface of the cup-like member to which the said electrode is fixed and which is also prevented from undergoing tilting displacement by additional locating means integral with the said cup-1ike member, and forming the envelope of the discharge tube by joining the said cup-like members together in such a manner that one of the said electrodes is positioned laterally by contact thereof with the apices of the protuberances on the cup-like member to which it is not fixed and is prevented from undergoing tilting displacement by the said additional locating means of the last-mentioned cup-like member, whereby the said electrodes are accurately positioned in desired spatial relationship to one another, and wherein, the said additional locating means comprises the formation of steps Onsome 9 or the said set of protuberances, which steps are adapted to prevent longitudinal movement of the associated electrode to -provide full spatial relationship,

12. A method of constructing an electric dischargetube having a glass envelope comprising two portions joined together, each of which carries at least one electrode complementary with an electrode of the other, wherein the said two portions of the envelope are each formed with locating means including inwardly projecting pro tuberances and relative to which locating means its said electrode can be mounted in only one exactly predetermined location; mounting the said complementary electrodes in each portion of the envelope in such predetermined locations, said locating means also providing complementary location so that the two said portions, with their electrodes, are interlocating, whereby they can only be assembled with such complementary electrodes in one predetermined relative transverse spatial relationship, at least some of the said protuberances being formed separately by indentation from the exterior with a suitable tool at previously locally softened parts of the said cup-like members, the protuberances being formed to a height determined by a mandrel within the cup-like member concerned.

13. A method of constructing an electric discharge tube including the fixing into each of two glass cup-like members of an electrode which, during the fixing process, is prevented from undergoing lateral displacement by the apices of a set of protuberances formed on pre-selected parts of the inner surface of the cup-like member to which the said electrode is fixed and which is also prevented from undergoing tilting displacement by additional locating means integral with the said cup-like member, and forming the envelope of the discharge tube by joining the said cup-like members together in such manner that one of the said electrodes is positioned laterally by contact thereof with the apices of the protuberances on the cup-like member to which it is not fixed and i prevented from undergoing tilting displacement by the said additional locating means of the last-mentioned cup-like member, whereby the said electrodes are accurately positioned in desired spatial relationship to one another, wherein at least some of the said protuberances are formed separately by indentation from the exterior with a suitable tool at previously locally softened parts of the said cup-like members, the protuberances being formed to a height determined by a mandrel within the cuplike member concerned.

14. A method of constructing an electric discharge tube havinga glass envelope comprising two portions joined together, each of which carries at least one electrode complementary with an electrode of the other, wherein the said two portions of the envelope are each formed with locating mean including inwardly projecting protuberances and relative to which locating means its said electrode can be mounted in only one exactly predetermined location; mounting the said complementary electrodes in each portion of the envelope in such predetermined locations, said locating means also providing complementary location so that the two said portions, with their electrodes, are interlocating, whereby they can only be assembled with such complementary electrodes in one predetermined relative transverse spatial relationship, at least some of the said protuberances being formed by fusing glass beads ill tothe intrior ofsald' cupdike members and adjusting in h'eightby means of a mandrel whilst the beads are in a plastic state. -1'5.-A method of constructing an electric discharge tube including the fixing into each of two cup-likem'embers of an electrode which, during the fixing DIQWS is prevented from undergoing lateral displacement by the apices of a set of protuberances formed on pre-selected parts of the inner-surface of thecup-Iike member to which the said electrodeis fixed and which is also prevented from undongoing tilting displacement by additional-locating.means integral with the said cup-like member, and forming theenv'elopeof the discharge tube by joining the said cup-like members together in such manner that one of the said electrodes is positioned laterally by contact thereof with the apices of p otuberances on the cup-like member to which it is not fixed and is prevented from undergoing tilting displacement by the said additional locating means of the lastmentioned cup-like member, whereby the said electrodes are accurately positioned in desired spatial relationship to one another, wherein at least some of the said protuberances are formed by fusing glass beads to the interior of said cuplike members and adjusting in height by means of a mandrel whilst the beads are in a plastic state.

16. An electric discharge tube comprising a glass envelope consisting of two cup-like members, each of said members having internal protuberances, one of said members having an electrode sealed into the same, the position of said electrode being fixed relative to but spaced from said protuberances, the other member having a second electrode sealed into the same in contact with the protuberances thereof, the open ends of said members being fused together to seal said tube.

17. An electric discharge tube comprising a glass envelope consisting of two cup-like members, each of said members having internal Drotuberances, one of said members having an electrode sealed into the same, the position of said electrode being fixed relative to but spaced from sealed into the same, the position of said electrode a being fixed relative to but spaced from said protuberances, the other member having a second electrode sealed into the same in contact with the protubrances thereof, the open ends of said members being fused together to seal said tube, said second electrode being also in contact with the protuberances of said first member, said second electrode being positioned against lon itudinal displacement by the protuberances of both said members.

19. An electric discharge tube comprising a glass envelope consisting of two cup-like members, each of said members having internal protuberances, an anode mounted within one of said cup-like members and positioned accurately by non-contacting reference to the apices of said protuberances thereon and having a lead-in wire passing through the bottom of said first cup, the

other cup-like member having a :cathode posi- REFERENCES .cnEn

The following references are "of recordin the file of this patent:

UNITED STATES PATENTS Number Name Date 1,295,481 Greiner et a1 Feb. 25, 1919 2,074,864 Salzberg Mar. 23, 1937 2,268,670 Ronci Jan. 6, 1942 2,194,432 Pomfrett Mar. 19, 1940 2,310,983 Miller Feb. 16, I943 FOREIGN PATENTS Number Country Date 507,840 British Nov. 19, 1937 

